Because of their great efficacy, high-pressure sodium discharge lamps have become a staple source of highway and area lighting. One of the more difficult, time-consuming processes in the manufacture of a high-pressure sodium lamp is the proper insertion and placement of the electrode structure in the end plug, the placement of the electrode within the arc tube body, and the sealing of the end plug to the arc tube.
In U.S. Pat. No. 3,992,642 dated Nov. 16, 1976 and issued to McVey et al., there is disclosed a coiled member which is part of or attached to the metal lead wire extending through the aperture in the ceramic plug which provides support for the electrode within the arc tube and thermal isolation of the lead wire seal from the electrode.
In U.S. Pat. No. 4,034,252 dated July 5, 1977 and issued to McVey, there is disclosed a cross piece member which is attached to the metal lead wire proximate the alumina plug on the opposite side of the aforementioned metal coil support member. This cross piece, which is spot welded to the lead wire, maintains the electrode coil and lead wire in a fixed position relative to the alumina plug, and forms a wick equalizing the distribution of sealing frit between the plug seal and the in-lead seal. It also serves as a hanger for supporting the plug and electrode assembly in the arc tube during sealing.
The invention described in the above patent requires that the cross piece be welded to the lead wire before the cross piece can be relied upon to secure the electrode assembly in its location or prevent the alumina plug and electrode assembly from falling into the arc tube. The single cross piece member also provides only two-point suspension and does not define a plane within which the alumina plug is held nor does it center the electrode assembly within the aperture in the alumina plug.